Roller screen conveyors having a plurality of spaced apart rollers are typically used to size or grade material being conveyed by and over the rollers. By changing the amount of spacing between adjacent rollers, oversized material, undersized material or both may be separated from the desired material size. Various materials may be graded by a conveyor screen; green iron ore pellets being a prime example. Typically, the rollers closest to the feed end of the conveyor are spaced so that undersized material will drop through the space therebetween. The remaining rollers are spaced for the desired material size. The oversized material, unable to fall between the rollers, is discharged off the end of the conveyor screen.
In order to be able to change the sizing of the material desired or to correct for wearing of the surface of the rollers, the spacing between the rollers must be adjustable. Various techniques have been developed to accomplish this adjustment. One approach requires that each roller is individually adjustable; a second approach utilizes simultaneous adjustment of spacing for a group of rollers. U.S. Pat. No. 3,848,741 is an example of this first approach while U.S. Pat. Nos. 483,225, 1,325,505, 2,365,822 and 3,367,494 are examples of the second. A variation of the second approach allows for the simultaneous and unequal adjustment of the rollers. Pivoting linkages, nonlinear or multiple pitch screws are some of the means used to accomplish this result. Examples of this variation are given in U.S. Pat. Nos. 1,484,025, 4,148,398 and 4,209,097. While these patents all illustrate adjusting devices for changing the spacing of rollers on a roller screen conveyor, these devices do not possess the capability of permitting any adjustment in the spacing between any two adjacent rollers without affecting the spacing between any of the other remaining rollers.